7 Sep 2017

Bringing Kirk's tree daisy back to Wellington

From Our Changing World, 9:06 pm on 7 September 2017

An ambitious conservation project is bringing one of Wellington region’s most threatened plants back to the city.  It’s taken many years, but the first kohurangi seedlings are going back in the ground – and even up some trees.

Tree climber planting kohurangi

Tree climber planting kohurangi in sacking pockets on old macrocarpa trees at Zealandia ecosanctuary. Photo: RNZ / Alison Ballance

Suspended high above Wellington’s Zealandia ecosanctuary, a climber staples a piece of sacking to the trunk of an old macrocarpa tree. Having made a pocket, he pours some potting mix in, adds a small plant and gently taps the soil around it.

On the ground below, botanist Chris Horne wields a shovel as he digs a hole large enough to take a punga pot. That pot will be a raised pedestal housing another small seedling.

Watching over operations is Finn Michalak, nursery curator at Wellington’s Otari Wilton’s Bush.  He and colleague Rewi Elliot have been working for years on this ambitious project to bring kohurangi back to Wellington City.

Kohurangi is a tree daisy. It has large glossy leaves, and when it flowers it is covered in a spectacular mass of white blooms. It grows as a shrub that can be about a metre high and a metre across - but most plants don’t make it to adulthood.

It is what botanists call ‘an ice cream plant’ - a favourite food for goats and deer, and probably pigs and possums. As a result it is now uncommon in the lower North Island and is classified under the Department of Conservation's species threat classification as ‘at risk – declining’.

Kirk's tree daisy in a wire cage

The tree that this Kirk's tree daisy was perching on crashed to the ground, and rangers planted it and put it in a wire cage to keep it safe from deer and goats. It lives on a high misty ridge. Photo: RNZ / Alison Ballance

Kohurangi or Kirk’s tree daisy (Brachyoglottis kirkii var. kirkii) is so rare that Greater Wellington Regional Council ecologist Owen Spearpoint can tell you the location of each individual adult in Wellington. He knows of a dozen or so in the upper Orongorongo Valley, which forms part of the Wainuiomata water catchment, and another dozen or so in the Akatarawa Range.

Kohurangi grows on high misty ridges. It requires lots of sun so often grows as an epiphyte, perched in the branches of large trees, and this lofty habit has undoubtedly saved the species from the ravages of browsing herbivores.

One of the largest known plants, however, has been growing on the ground in the upper Orongorongo Valley since its host tree fell over. It gets enough sun on the side of the road, and is fully protected in a wire cage.

One of the problems in the wild, though, is that individuals are so scattered that the chance of insects successfully moving pollen between plants is negligible. This plant’s nearest neighbour, for example, is several hundred metres away.

Growing kohurangi

Almost a decade ago, kohurangi’s rarity brought it to the attention of the team at the Otari Wilton’s Bush’s nursery, who were keen to help in the conservation of rare plants in the region. Nothing was known about how to grow kohurangi but the team had plenty of experience to call on.

The plant in the cage has provided some of the seeds and cuttings that Finn Michalak and Rewi Elliot have collected and tried to grow over the years. Their initial attempts to grow kohurangi from seeds collected in the wild failed. But the cuttings did take in cultivation – and seeds from those initial plants were successfully germinated and grown on.

It’s always a challenge to grow kohurangi, as the seedlings are prone to rotting. This has largely been solved by the use of a natural antifungal product called Neem.

For a while it was difficult to get seeds to germinate, until the team struck on the idea of using moss collected from the forest. During a hunt for more wild plants, they found some seedlings successfully growing on the ground in thick mats of moss and kidney ferns and this proved to be an ideal medium for baby kohurangi.

Rewi also came up with a novel way to plant kohurangi in the ground to ensure they didn’t suffer stem rot from wet soil. It was a technique he had developed with Vireya rhododendrons, which are also perching plants. A length of hollow punga stem is partly dug into the ground, and the seedling is planted within that raised pot.

Rewi Elliot and Finn Michalak

Rewi Elliot and Finn Michalak with different sized seedlings of Kirk's tree daisy that have been grown in the Otari Wilton's bush nursery. Photo: RNZ / Alison Ballance

Into the ground - and up a tree

This winter, 100 kohurangi were planted out in Otari Wilton’s Bush, and at nearby Zealandia. Otari Wilton’s Bush still has issues with possums, while Zealandia is completely free of introduced herbivores, and the success of plants at the two sites will be monitored.

Some were planted in trees, others in punga pots and some in the ground, and again, the survival rates of plants will be compared to see which is the best method.

All the kohurangi have been planted in an easily accessible part of Zealandia, to allow the public to watch the plants grow – and hopefully flower.

Kohurangi seedlings ready for planting.

Kohurangi seedlings ready for planting. Photo: RNZ / Alison Ballance

Meanwhile, a search in the wild last summer turned up several clumps of new seedlings, sprouted from seeds that had blown onto the forest floor. Some of these have been protected with wire cages, and the joint kohurangi conservation team will keep an eye on their survival.

In future, Rewi and Finn hope that some of the kohurangi they have grown will be planted back into the wild, to boost the natural populations. And who knows, maybe one day kohurangi might also be available for keen gardeners, with garden populations offering another insurance for the plants’ survival.

A small kohurangi plant (the large leaved plant in the middle of the photo) has survived on top of a steep road cutting, where it is probably out of reach of deer and goats.

A small kohurangi plant (the large leaved plant in the middle of the photo) has survived on top of a steep road cutting, where it is probably out of reach of deer and goats. Photo: RNZ / Alison Ballance